Dietary Zinc Intake and Urinary Zinc Excretion in Diabetic Nephropathy

Abstract

As nephropathy appears to increase the risk of zinc deficiency, the purpose of this study was to determine if there was a difference in reported dietary zinc intake and urinary zinc excretion between Type I and Type II diabetics exhibiting nephropathy. Thirteen subjects (Type I, n=6 and Type II, n=7) with creatinine clearance less than 50 mL/hr, and greater than or equal to 3 g proteinuria were studied for 7 days. The subjects completed a 7 day food diary which was used to determine dietary zinc and protein intake. A 24 hr urine collection taken on day 3 was used to determine creatinine clearance and urinary zinc excretion. Urinary zinc was measured by inductively coupled plasma emission spectroscopy at the Mayo Clinic in Rochester, MN. The use of medications (ACE inhibitors and diuretics) pertinent to urinary zinc excretion was noted. The food dietary analysis indicated that without supplementation only 19% of the population met the RDA for zinc; 46% of the population met the RDA for zinc when a multivitamin with zinc was included on a regular basis. Of the seven subjects who exceeded the RDA for protein, five did not meet the RDA for zinc. The students t test showed no significant differences in reported dietary protein and zinc intake and medication use between Type I and Type II diabetics. Type II diabetics had a greater mean urinary zinc excretion (987.7±508.3 μg) than Type I diabetics (504.0±167.4 μg) (p=0.05); normal urinary zinc is 300-600 μg. These results suggest that the majority of the population studied was not meeting the recommended zinc intake from dietary sources and that an adequate protein intake does not assure that the zinc RDA will be met. Findings indicate Type II diabetics may be at risk for zinc deficiency relative to their low dietary zinc intake and greater urinary zinc excretion. Further research in this population may confirm that zinc supplementation may be beneficial in clinical practice.